<!DOCTYPE html>
<html lang="en">

<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Document</title>
</head>
<style>
	.flexbox {
		display: flex;
		width: 400px;
		height: 250px;
		background-color: lightgrey;
	}

	.item {
		background-color: cornflowerblue;
		width: 100px;
		height: 100px;
		margin: 10px;
	}
</style>

<body>
	<div class="flexbox">
		<div class="item">item1</div>
		<div class="item">item2</div>
		<div class="item">item3</div>
	</div>

</body>

</html>